How to replace the launch button from the native dialer to Orange Phone app?

You just need to drag&drop the Orange Phone app icon to put it on the welcome screen of your device.

Some models of device also allow the user to update the app shortcuts in the lock screen, on which you can then select the dialer app as a shortcut.

You may need to reboot your device to take into account the shortcut in the lock screen. For more information, check the notice of your device.